The present invention generally relates to methods of driving ink jet type printing heads, and more particularly to a method of driving an ink jet type printing head so that the printing quality is greatly improved at a low cost using the ink jet printing head which has a relatively simple construction.
A known ink jet type printing head is provided with a piezoelectric element, and the ink is ejected when the piezoelectric element is activated. According to the so-called on-demand type ink jet printing system which controls the ink ejecting pressure, an electrical signal is applied to the printing head, and this electrical signal is converted into pressure waves by the piezoelectric element so that the ink is ejected by the pressure waves. This on-demand type printing system generates pressure pulses depending on the electrical signal, and thus, has advantages in that a driving circuit having a simple construction can be used. Examples of the on-demand type ink jet printing systems are disclosed in the Japanese Published Patent Application No. 2-24218 and the Japanese Laid-Open Patent Application No. 62-56150.
The Japanese Published Patent Application No. 2-24218 proposes a method of driving the on-demand type ink jet printing head. A driving voltage pulse in the same direction as the polarization voltage is applied in advance to the piezoelectric element to accumulate a charge and reduce the volume of a pressure chamber. When ejecting the ink, the charge is gradually discharged to increase the volume of the pressure chamber, and a pulse is thereafter applied again to quickly accumulate a charge and reduce the volume of the pressure chamber so as to eject the ink. Hence, the printing head can be driven by an inexpensive driving circuit, and the ink can be ejected by use of a relatively low driving voltage. However, no consideration is given as to the mutual interference introduced in a multi-nozzle printing head, and there is no teaching with regard to controlling the phase of the driving voltages applied to the nozzle parts of the printing head.
On the other hand, the Japanese Laid-Open Patent Application No. 59-176060 proposes to provide electrodes for applying first and second voltages and to contract a side wall part when expanding an actuator part. But this arrangement requires additional electrodes to be formed and an additional driving circuit. Furthermore, there is no teaching with regard to controlling the phase of the driving voltages applied to the nozzle parts of the printing head.
Therefore, there is a demand to realize a method of driving the ink jet type printing head, which enables stable ejection of the ink and suppresses deviation in the ejection velocity of the ink with respect to the driving frequency. Further, it is also desirable to realize a method which prevents deterioration of the ink ejection velocity caused by mutual interference of the nozzles of the multi-nozzle printing head when the nozzles are simultaneously driven.